Gold-coated ZnO nanostructures on no-core optical fiber for ammonia detection in food spoilage applications.

A selective and cost-effective optical fiber sensor for detecting ammonia gas, a key byproduct of food spoilage, was developed using a no-core fiber (NCF) structure. The optical fiber was coated with a zinc oxide (ZnO) thin film decorated with gold nanoparticles (AuNPs) to enhance sensitivity and selectivity. Four sensor configurations were fabricated with varying AuNP concentrations (0.1 mM and 1 mM) and ZnO nanostructure morphology (nanoparticles and nanorods) and tested with ammonia (NH₃) gas concentrations ranging from 0.15 to 10 ppm, a typical range for food spoilage. The sensor functionalized with 0.1 mM AuNPs and ZnO nanoparticle exhibited the best performance, achieving a sensitivity of 0.093 nm/ppm, a limit of detection (LOD) of 0.96 ppm, a response time of 60 s, and a recovery time of 90 s. Mixed gas experiments demonstrated the sensor's strong selectivity for ammonia, even in the presence of other volatile compounds such as isopropanol, ethanol, and acetone. Tests under varying temperature (21-27 °C) and humidity (45-75% RH) confirmed stable sensor response, with negligible effect on sensitivity. These results highlight the sensor's potential as an effective and reliable tool for detecting food spoilage.